Cathode bat tube



March 3, 1936. c. P. MARSDEN CATHODE RAY TUBE Original Filed June 2, 1933 Md KM INVENTOR ATTOR N EY sis, etc.

Patented Mar. 3, l936 UNITED STATES CATHODE BAY TUBE Charles P. Marsden, Bloomfield, N. 3., assignmto Hygrade Sylvania Corporation, Salem, M,

a corporation of Massachusetts Application June 2, 1933, Serial No. 674,047 Renewed July 5, 1935 5 Claim.

A further feature relates to the method of at,-

taching the fluorescent coating to the glass or other similar body.

Other features and advantages not specifically enumerated will be apparent after a consideration of the following detailed description and appended claims.

While the invention finds its greatest practical advantages in the manufacture of so-called cathode ray tubes or Braun tubes, the inventive method is not limited to the manufacture of any particular kind of tube, but is capable of application in any' situation where a uniform coating of fluorescent material is to be applied to a supporting member.

In certain types of apparatus, for example cathode ray tubes, Braun tubes, or the like, there is provided a screen which comprises a material that fluoresces or emits light when bombarded by cathode rays or the like. For example, in one known type of construction employed for this purpose, the tube is provided with a constricted or neck portion at amend and an enlarged, substantially flat screen portion at the opposite end, the interior face of this screen portion being provided with this fluorescent coating. Suitable electrodes are provided within the tubefor generating, accelerating and oscillating the beam of cathode rays which, upon striking the screen, causes the latter to fluoresce or otherwise emit light rays. Such tubes are customarily used as oscillographs for wave analysis, frequency analy- Tubes of this general type have also been. employed for television or picture trans mission purposes, in which case the beam or cathode ray not only hasits spacial position varied in synchronism' with a transmitter, but also the intensity and/r velocity and/or width of the impinging beam are varied to correspondingly vary the intensity-ofthe fluorescent effect from the screen. While, for oscillograph or similar uses it is important that the fluorescent coating be uniform, minor variations of thickness or uniformity of the grain in the coating do not seriously affect results. However, in television or similar uses it is absolutely necessary, if truly faithful images are to be reproduced, that the fluorescent coating be not only of the highest uniformity as to thickness, but it is also important that the individual grains constituting the coating be, as far as possible, of the same degree of fineness. It is further highly important in all types of cathode ray tubes that the fluorescent coating be firmly united to the glass or other support, since it is required to be bombarded continuously by the cathode rays.

Various methods have heretofore been proposed for applying the fluorescent coating. For example, the most common way is to mix the fluorescent coating with a suitable binder which is then sprayed over the surface to be coated. Needless to say, with ordinary spraying methods it is extremely diificult to secure a coating of uni- 0 form thickness. This may be due to a variety of causes. For example, in spraying it is required that the material be sprayed onto the receiving surface at substantially-right angles, with the result that if a non-uniform or large grain of material attaches itself to the supporting surface, succeeding traverses of the spray aggravate and accentuate the thickness of the coating at this point. Added to this is the fact that if the coating is not evenly united to the support over its 0 entire surface, the force of the spray may dislodge one or more grains from the coating. Other methods such as painting or the like obviously are incapable of producing uniform coats because of the appreciable physical dimensions of the painting tool as compared with the fine grain constituting the coating.

It has been found that a thoroughly uniform fluorescent coating may be achieved in accordance with this invention without spray, painting or similar processes.

In accordance with the invention the surface of the tube to be coated is first provided with a the said film, thus distributing the fluorescent s5 powdered material in an even depout over the film. The excess of powdered material may then be removed by pouring or similar process, after which the support may be heated, baked, or fired to a dull red heat to remove the film and/or binders, resulting in a firm attachment of the fluorescent material onto the glass or other support.

While the foregoing description gives a general plan of the preferred procedure to be employed, a detailed description will now be given of the manner of practicing the invention in connection with a typical form of cathode ray tube.

Referring to the drawing, the numeral I indicates generally a glass or other tube having a constricted or neck portion 2 and a flared or enlarged portion 3. The portion 3 terminates in a substantially flat portion 4 which serves to carry the fluorescent material. In accordance with well-known practice in the art of cathode ray tube design, the tube I is provided with an emitting cathode represented schematically by the numeral 5, and an electrodeor electrodes 6 fo'r varying the intensity of the cathode ray beam. A concentrating or focusing electrode 1 is usually provided to restrict the beam to a comparatively narrow width. A pair of vertical deflecting plates 8 and a pair of horizontal deflecting plates 9 (one shown) are provided for oscillating the cathode ray beam over any predetermined path. A suitable anode or anodes III are provided for accelerating the electrons from the cathode 5. The manner of producing and oscillating the cathode ray beam above described constitutes no feature .of the present invention and any well-known means may be provided for this purpose.

Prior to attaching the constricted or neck portion 2 to the flared portion I, the latter flared portion 3 has the interior surface of the wall 4 provided with a tenuous film preferably of the nature of a plasticised lacquer indicated in the drawing by the numeral II. It is preferred to employ a binder consisting, for example, of a solution'of nitro cellulose in a volatile solvent, e. g., ethyl carbonate, amyl acetate, etc. This binder solution is then plasticised preferably by mixing with it 1 dibutyl phthalate, and in order to retard the drying, a small percentage,

such as 1% of diethyl oxalate may be mixed with the binder. It is to be understood, of course, that the inventio'n is not limited to this particular plasticising agent. For example any diamyl or diethyl phthalate or phthalates may be employed or, if desired, dicresyl phosphate may be employed. The invention also contemplates the use of lacquer films containing gums, if these latter gums are burnt out in the flnal firing. As above stated, the plasticised film is preferably of a tenuo'us character or'suiflciently thin so as-to be substantially completely transparent, although it will beunderstood that any other known transparent film may be employed which, upon flring, is completely removed or becomes transparent.

The fll-m is preferably deposited by pouring or other similar operation. For example, if the portion 4 of the tube is five inches in diameter, ap-'- proximately 2 cc. of the above material may be dropped on the interior face of the portion 4 and allowed to flow evenly over the surface. Any excess of the material over the required amount may be drained off in any suitable manner, with the result that there is produced a tenuous uniform film which is substantially free from bubbles, flowing marks, etc. This fllm is then allowed to dry or is dried to the point where it becomes appreciably tacky or sticky, and the excess of material around the edges may be wiped off or otherwise removed. The drying is then carried slightly further, by blowing a gentle current of air into the bulb until the odor of the solvent: has substantially entirely disappeared.

After this treatment the film II is in a condition such that it will just show finger prints and is now in condition to receive the powdered fluorescent material. Any well-known fluorescent material such as ordinarily employed in cathode ray tubes or the like may be employed. Preferably this material is intimately mixed with a weighty powdered zinc of about 30 mesh. The mixed powdered materials are then poured into the bulb and the bulb is swirled, oscillated, and somewhat violently shaken so as to distribute the relatively fine fluorescent material in an even deposit over the sticky film ll. As a result of this agitating process the heavy grains or particles of zinc or other weighty material cause the powdered fluorescent material to be dis- ,tributed in a uniform layer over the film ll.

One possible explanation for this is that the "very fine particles of the fluorescent material are held by a sufllcient adhesive force to prevent their dislodgment by the moving or swirling weighty-particles of zinc, whereas the non-uniform or enlarged grains of the fluorescent material are carried by the swirling or agitated weighty material, with the result that the fluorescent coat which finally adheres to the film ll The material having thus been removed, theedges of the coating may be trimmed by rotating the bulb and wiping off the material with a cloth or rubber scraper.

45 The ned 4 of the tube is then subjected to heat preferably to raise it to a dull red heat or to a temperature at which the binder and/or the plasticized film II is removed. Preferably also the heat is maintained for a suflicient length of time to bake the fluorescent material onto the member 4. I

A tube prepared in accordance with the above coating has been found to possess extremely uniform graining and thickness of fluorescent material and it will be obvious, of course, that varlous changes and modifications may be made in the described procedure without departing from the spirit and scope of the invention. For example, if desired, the portion 4 of the tube may be slightly heated while pouring in the plasticised lacquer, and this heating may be gradually increased until the film is entirely removed.

If desired, the above procedure may be repeated so as to provide successive coats of fluorescent material, each coating having a thickness practically consisting of a single grain.

The portion 3 thus prepared may then -be united or sealed to the neck portion 2 and the tube may then be subjected to the ordinary evacuation and treatment customarily employed in the manufacture of vacuum tube and electron tube devices in general.

What I claim is:

1. A cathode-raytube having an enclosing envelope with a flattened end m. a cathode, an anode and a deflecting electrode mounted within said envelope, and a coating on the interior surface of said wall consisting of a transparent baked fllm of a plasticised lacquer carrying a powdery fluorescent material.

2. A cathode-ray tube having an enclosing 'envelope with a flattened end wall, a cathode, an anode and a deflecting electrode mounted within said envelope, and a coating on the interior surface of said wall consisting of a transparent baked fllm of a lacquer containing a phthalate plasticiser and carrying a powdery fluorescent material on its exposed surface.

3. A cathode-ray tube according to claim 2 in which the plasticiser is a diamyl phthalate.

4. A cathode-ray tube according to claim 2 in which the plasticiser is a dibutyl phthalate.

5. A cathode-ray tube according to claim 2 in which the plasticiser is dicresyl phosphate.

CHARLES P. MARSDEN'. 

